This invention relates to a heat transferable sheet or a sheet to be heat transfer printed, more particularly to a heat transferable sheet to be used in combination with a heat transfer sheet for performing image formation by heating printing means such as thermal head.
In the prior art, as methods for forming printed images according to the heat transfer method, the following methods have been proposed. That is, various studies have been made on the method in which, by the use of a heat transfer sheet comprising a heat transfer layer containing a meltable or sublimatable dye formed by heating on a substrate sheet and a heat transferable sheet having a receptive layer for receiving the dye which as migrated from the heat transfer sheet, superposing these sheets so that the heat transfer layer will contact the receptive layer, and imparting heat energy by means of a spot heating means such as a thermal head, which generates heat corresponding to the image information from the back side of the heat transfer sheet, the dye in the heat transfer layer is transferred to the receptive layer and images of natural color photographic tone are obtained.
For heat transferable sheets to be used for such purpose, we have made various proposals in which receptive layers such as of saturated polyesters are used on the surface of synthetic papers.
A heat transferable sheet having a synthetic paper as a substrate sheet has excellent strength and flexibility as compared with a heat transferable sheet having a conventional paper as the substrate sheet but, on the other hand, it has the following problems. The heat transferable sheet as mentioned above, of which, the synthetic paper itself is used for the substrate sheet is constituted of resin components with relatively low heat resistance such as polyolefin resins, suffers from residual strain caused in the substrate sheet by the heat energy applied during image formation, whereby a problem arises in that the heat transferable sheet is curled after image formation.